1. Field of the Invention
Embodiments described herein relate generally to a charged particle beam writing apparatus and a method for acquiring a dose modulation coefficient of a charged particle beam, and for example, relates to an apparatus and a method for making resist heating corrections.
2. Related Art
Writing technology in charge of developing still finer semiconductor devices is, among semiconductor manufacturing processes, an extremely important process that generates patterns as the only one process. In recent years, with an ever higher degree of integration of LSI, circuit line widths demanded from semiconductor devices become finer year by year. A high-precision original pattern (also called a reticle or a mask) is needed to form a desired circuit pattern on these semiconductor devices. An electron beam (EB) writing technology has inherently superior resolving properties and is used to manufacture high-precision original patterns.
FIG. 8 is a conceptual diagram illustrating an operation of a conventional variable-shaped electron beam writing apparatus.
The variable-shaped electron beam writing apparatus operates as described below. A first aperture plate 410 has a rectangular opening 411 to shape an electron beam 330 formed therein. A second aperture plate 420 has a variable-shaped opening 421 to shape the electron beam 330 having passed through the opening 411 of the first aperture plate 410 to a desired rectangular shape formed therein. The electron beam 330 having passed through the opening 411 of the first aperture plate 410 after being irradiated from a charged particle source 430 is deflected by a deflector and passes through a portion of the variable-shaped opening 421 of the second aperture plate 420 before a target object 340 mounted on a stage continuously moving in one direction (for example, assumed to be the X direction) being irradiated by the electron beam 330. That is, a rectangular shape capable of passing through both of the opening 411 of the first aperture plate 410 and the variable-shaped opening 421 of the second aperture plate 420 is written in a pattern writing region of the target object 340 mounted on the stage continuously moving in the X direction. The method for creating an arbitrary shape by causing a beam to pass through both of the opening 411 of the first aperture plate 410 and the variable-shaped opening 421 of the second aperture plate 420 is called the variable-shaped method (VSB method).
With the development of optical writing technology and shorter wavelengths due to an extreme ultraviolet (EUV), the number of shots of an electron beam needed to write a mask is increasing at an accelerated pace. On the other hand, shot noise and edge roughness of patterns are reduced by making a resist less sensitive and increasing the dose to ensure the precision of line width needed for micropatterning. Thus, the number of shots and the dose increase boundlessly and so the pattern writing time also increases boundlessly. Therefore, reducing the pattern writing time by increasing a current density is discussed.
However, if an increased irradiation energy amount is irradiated in a short time as a denser electron beam, a problem of phenomenon called resist heating is caused in which the substrate temperature is heated and resist sensitivity is changed, resulting in worse precision of line width. Thus, to solve such a problem, the inventors and the like have applied for a patent a technique of calculating a representative temperature for each minimum deflection region of deflection regions based on heat transfer from other minimum deflection regions written before the minimum deflection region and modulating the dose using the representative temperature (see Published Unexamined Japanese Patent Application No. 2012-069675 (JP-A-2012-069675), for example). Dimensional variations of patterns due to resist heating have been suppressed by making corrections in minimum deflection region units, instead of shots units, according to such a technique to perform a correction operation (temperature correction operation) at a higher speed.
In electron beam pattern writing, on the other hand, when a circuit pattern is written by irradiating a mask to which a resist is applied with an electron beam, a phenomenon called the proximity effect by back scattering in which the electron beam is transmitted through a resist layer to reach the layer thereunder before reentering the resist layer occurs. Accordingly, dimensional variations in which when a pattern is written, the pattern is written in dimensions deviating from desired dimensions occur. To avoid such a phenomenon, a proximity effect correction operation is performed by the writing apparatus to, for example, modulate the dose to suppress such dimensional variations.
However, even if the dose is modulated by performing a proximity effect correction operation, a problem of remaining correction residual is caused if thereafter, dose modulation to suppress dimensional variations due to resist heating is performed by performing aforementioned temperature correction operation.
In addition to the aforementioned temperature correction operation and dose modulation such as the proximity effect correction operation, the necessary dose is divided into a plurality of times of pattern writing by performing multiple pattern writing in electron beam pattern writing to suppress a temperature rise. The multiple pattern writing is frequently performed by shifting the position of a deflection region and in such a case, the aforementioned temperature correction operation needs to be performed for each pass (one-time pattern writing of multiple pattern writing) of multiple pattern writing because the position of the deflection region is shifted. Thus, if a proximity effect correction operation is combined therewith, the operation technique becomes still more complex and a problem of difficulty of a real-time correction operation is caused. Thus, process efficiency needs to be increased.